Physics PreLab- Electrostatistics

What are the three methods of charging-explain each.

What is an electrophorus and how does it work?

When you rub a balloon on your wool shirt, what charge does the balloon attain? What charge does the wool sweater attain?

Go to the lightning website and answer the following:

            How hot does air get when Lightning passes through it?

            What do we see when lightning occurs: the initial stroke or the return stroke?

Two identical 18 μC charges are separated by 17 cm. What is the electrostatic force between them?

A 75 kg student jumps off a bridge with a 12-m-long bungee cord tied to his feet. The massless bungee cord has a spring constant of 430 N/m. a. How far below the bridge is the student’s lowest point? b. How far below the bridge is the student's resting position after the oscillations have been fully damped?

We can show why we don’t have observable radial acceleration effects even though the Earth is

spinning and we can com

ment quickly on the tangential acceleration we experience.

a)

Specifically, show that Cleveland’s centripetal (i.e., radial) acceleration due to the earth’s

rotation is negligible in comparison with the acceleration we feel due to gravity.

Put your

answe

r in “gees” for a direct comparison.

b)

By the way, what is our angular acceleration in Cleveland? (Hoohah!) And therefore what

is our tangential acceleration?

A very thin circular disk of radius R = 17.00 cm has charge Q = 50.00 mC uniformly distributed on its surface. The disk rotates at a constant angular velocity ? = 5.00 rad/s around the z-axis through its center. Calculate the magnitude of the magnetic field strength on the z axis at a distance d = 1.700 × 10^3 cm from the center. Note that d >> R.

• In this lab you will take data from a video and attempt to verify the Law of Conservation of Momentum. Additionally, you will take into account the uncertainty of (most of) the measurements.
  
  There is no such thing as a perfect measurement. All measurements have some amount of error. Some of that error comes from mistakes made while taking the measurement; by slightly misusing the equipment (for example, not perfectly lining up a ruler) or by misreading the equipment. As such, it is common to state the uncertainty of a measurement. This is done by using the plus/minus symbol; ±. The number following this symbol is the uncertainty. For example, the measurement "5.2 m ± 0.2 m" has an uncertainty of 0.2 m. Overall, this means: "We believe the value is 5.2 m, we acknowledge we are probably slightly incorrect, but we are supremely confident that the actual value lies between 5 m & 5.4 m."
  
  In this lab you will be asked to estimate one uncertainty yourself. The rest will either be given to you or you will calculate them using the formulas provided.
  

• Video & data table

  The video below shows a dart being fired into a cart (that is initially at rest). The beginning sequence was filmed at 240 frames per second and it took 10 frames for the dart to travel 31 cm. You can use this data to determine the dart's momentum prior to impact. For this calculation, we will assume that the values that were just stated (240 frames per second, 10 frames, & 31 cm) are all exact. Fill in the PRE-COLLISION DATA TABLE.
  
  After the collision, the frame rate is 60 frames per second. The video shows the cart (with the dart embedded in the foam block) moving forward. The frame counter has restarted so that the "X" on the cart is at 0 cm at frame zero. By advancing the video, determine at which frame the "X" reaches the 10 cm line and enter that data in the POST-COLLISION DATA TABLE. You'll also need to identify the frame uncertainty: How many frames could your data be off by? You can assume that the 10 cm & 60 frames per second are exact values.
  
  Other data that you need is stated below the video as well as the formulas for calculating speed uncertainty & momentum uncertainty. NOTE: LEAVE THE MASS IN GRAMS.
  
  Mass of dart = 6.1 g ± 0.1 g
  Mass of cart = 262.5 g ± 0.1 g
  Total mass = 268.6 g ± 0.2 g
  speed uncertainty =

  speed × frame uncertainty

  # of frames

  momentum uncertainty = mass uncertainty × speed + mass × speed uncertainty

  
  Frame uncertainty =  
  

  PRE-COLLISION DATA TABLE	# of frames needed for dart to travel 31 cm	Δt (s)	vdart,i (m/s)	vdart,i uncertainty (m/s)	pdart,i (g·m/s)	pdart,i uncertainty (g·m/s)
  Dart	10			0

  POST-COLLISION DATA TABLE	# of frames needed for cart to travel 10 cm	Δt (s)	vf (m/s)	vf uncertainty (m/s)	pf (g·m/s)	pf uncertainty (g·m/s)
  Cart + dart

• Momentum range

  Using the values you calculated for momentum & momentum uncertainty, state the range for the pre-collision momentum & the post-collision momentum in the table below.

  	minimum momentum (g·m/s)	maximum momentum (g·m/s)
  Dart (pre-collision)
  Cart + dart (post-collision)

  
  Ideally, these ranges will overlap. The claim is that momentum is conserved. Within experimental error, you have shown this is true for this collision.

• Post-collision velocity

  By applying the Law of Conservation of Momentum to this situation, derive a formula for v_f. Your answer should be symbolic (no data). Use m for the dart mass, M for the cart mass, and v for the initial velocity of the dart.
  v_f =
  
  Using the formula you just derived, determine what v_f will be for the following three cases:
  
  M = 0 (cart mass is zero); v_f =
  M = m (cart & dart have same mass); v_f =
  M >> m (the cart mass is much greater than the dart mass); v_f =
  
  Using your data and the formula you derived (at the top of this section), calculate v_f.
  v_f =  
  
  Now determine the uncertainty of this value using the following formula: v_f uncertainty =

  dart mass uncertainty × dart speed

  total mass of cart & dart

  
  v_f uncertainty =  
  
  You have now determined v_f two different ways. In the POST-COLLISION DATA TABLE you determined it using distance/time. Just above, you determined it using conservation of momentum. Using the values & uncertainties you calculated for each, fill in the table below. As before, ideally the ranges will overlap.

  	minimum vf (m/s)	maximum vf (m/s)
  Determined using distance/time
  Determined using conservation of momentum

Three particles, charge q₁ = +12 µC, q₂ = -19 µC, and q₃ = +31 µC, are positioned at the vertices of an isosceles triangle as shown in the figure. If a = 10 cm and b = 5.7 cm, how much work must an external agent do to exchange the positions of (a)  q₁ and q₃ and, instead, (b)  q₁ and q₂?

1.) The femur of an elephant is about 90 cm long and 15 cm in diameter. This is a scaling problem. The largest dinosaur probably weighed about 10 times as much as a large elephant. In this problem we will be discussing scaling. For reference, areas scale as length squared(A=L^2 for a square and A=3.14*r^2 for a circle) and volume scales as length cubed. To describe the size of a dinosaur's femur compared to that of an elephant's, the dinosaur's femur appears to be 3 times as wide and one and a half times as tall.

a.) How do you expect the mass of an animal to scale with the length of typical bone? Use this to estimate the length of the dinosaur's femur.

b.) How do you expect the strength of a bone to scale with its width?(We want a uniform strain (delta L/L) for all animals.) Use this to estimate the width of the dinosaur's femur.

c.) Are your answers to a and b consistent with the description of the size of a dinosaur's femur stated above? Why or why not?

d.) Based on this, briefly argue why whales (2.5 times larger than the largest dinosaurs) are not land animals.

the following questions are pertaining to an ultrasound. what is the "illumination" source (where does the energy come from)? what interaction are you measuring (reflection, refraction, absorption)? what is the image detecting (what information do you get from the image)?

Hummingbirds can pick up static charge as they fly either from the air or from interactions with plants. A possible value is +250 pC.

a. Given this charge, did the bird gain positive charge or lose negative charge? Explain.

b. If we model the hummingbird as a sphere with the above net charge attained from the air with a radius of 2.9 cm, what is the electric potential or “voltage” at the bird and 5 cm away from the bird?

c. If we model the bird (charged through interactions with plants) as one side of a capacitor with the earth as the other side with the opposite charge, and the capacitance is 1.3 pF, what is the potential difference between the bird and the earth? (parts b and c are independent questions.)

The length of a simple pendulum is 0.72 m and the mass of the particle (the "bob") at the end of the cable is 0.21 kg. The pendulum is pulled away from its equilibrium position by an angle of 8.40° and released from rest. Assume that friction can be neglected and that the resulting oscillatory motion is simple harmonic motion.

(a) What is the angular frequency of the motion?
____rad/s

(b) Using the position of the bob at its lowest point as the reference level, determine the total mechanical energy of the pendulum as it swings back and forth.
____ J

(c) What is the bob's speed as it passes through the lowest point of the swing?

____m/s

Find the wavelength (in nm) of a photon whose energy is 9.00 × 10^-19 J.

Air that occupies a volume of 0.142m3 at a gauge pressure of 103kPa, expands isothermally to zero gauge pressure and then is cooled to constant pressure until it reaches its initial volume. Calculate the work done on the gas.
Answer: -5.74 kJ

A block of mass 5 kg rests on a 30° inclined plane. The surface is rough. The coefficient of friction between the surface and the block is 0.5. Find the frictional force exerted by the plane on the block. (N)

The dielectric in a capacitor serves two purposes. It increases the capacitance, compared to an otherwise identical capacitor with an air gap, and it increases the maximum potential difference the capacitor can support. If the electric field in a material is sufficiently strong, the material will suddenly become able to conduct, creating a spark. The critical field strength, at which breakdown occurs, is 3.0 MV/m for air, but 60 MV/m for Teflon.

Two blocks are connected by a light string that passes over a frictionless pulley having a moment of inertia of 0.0040 kg*m2 and a radius of 5.0 cm. The coefficient of kinetic friction between the table top and the upper block is 0.300. The blocks are released from rest. Using energy methods, find the speed of the upper block just as it has moved 0.600 m.